1. Field of the Invention
The present invention relates generally to a sheet brush seal providing a seal between a shaft and a relatively moving element. More particularly, the invention relates to a sheet brush seal used in airplanes, gas turbines or the like which provides a seal between a rotor shaft and a casing (opposing element) which moves relative to the rotor shaft due to a shaft vibration.
2. Description of the Related Art
There has been a brush seal device 100A as a relative art of the present invention as shown in FIG.15.
FIG.15 shows a cross sectional view of the brush seal device 100A which is disposed between a rotor shaft 120 and a casing 110 through which the rotor shaft 120 extends.
The casing 110 is an element which is securely fixed in a steam turbine or a gas turbine. The brush seal device 100A is installed in the casing 110 providing a seal of a process fluid over the rotary shaft 120.
The brush seal device 100A in FIG. 15 has a ring shape and its outer circumference portion which is defined as a mounting portion 104 is disposed in the fixture groove portion 112 of the casing 110. The brush seal device 100A is mainly comprised of a brush seal 109, a backing plate 112 and a support plate 103. Thickness of the brush seal 109 is determined by a plurality of strong brush bristles piled along the axial direction. This defines a ring shaped circular wall of the equal thickness. The outer circumferential end portion of a ring shape being integrated defines the mounting portion 104.
Also a free end face 105 of the brush seal 109 is disposed in an opposing manner relative to the rotor shaft 120. Diameter of the strong brush bristle 101 is generally chosen in a range from 0.02 mm to 0.5 mm, and the number of the brush bristles ranges from several ten thousands to hundred thousands.
The opposite face of the brush seal 109 relative to the process fluid is located in such a way that the face is kept in contact with a side face 108 of the backing plate 102 which has a donut shape, and the backing plate 102 gives a support to the brush seal 109 such that the brush bristles do not give way to the pressure exerted by the process fluid.
The backing plate 102 and a retaining plate 103 which is a circular ring shape securely clamp therebetween the mounting portion 104 of the brush seal 109. The width of the retaining plate 103 in a radial direction is arranged to be small so that the retaining plate 103 does not restrain the free end portion of the brush seal 109. As a result, the front face of the brush seal 109 is exposed to the process fluid side.
The backing plate 102, the mounting portion 104 of the brush seal 109 and the retaining plate 103 are welded together at their common ends to form an integral joint portion 106.
The straight brush bristles 101 shown in FIG. 15 are disposed along radial directions with respect to the diameter of the rotor shaft 120. The brush seal 109 under normal circumstances is in contact or nearly in contact with the rotor shaft 120 at its free end face 105.
As described above, the brush seal 109 retains a pack of brush bristles 101 being assembled along the circumferential direction to form a ring structure. And the free end face 105 of the brush seal 109 is subjected to a precision finish such as a wire EDM so that the end face 105 precisely fits the rotor shaft 120. The brush bristles 101, however, easily give way and it is extremely difficult to prepare the brush bristles 101 to such an extent that a tiny clearance is formed between the end face 105 and the rotor shaft 120.
In the brush seal device 100A constructed as mentioned above, the brush seal 109 is pressed against the rotor shaft 120 when a vibration or a swinging motion of the rotor shaft causes it to touch the brush seal 109.
Under this circumstance with a high process fluid pressure P1 in FIG. 15, an increased pressure differential P1-P2 relative to a lower pressure P2 induces the straight brush bristles 101 of the brush seal 109 to be forced to press against the backing plate throughout the entire portion of the bristles and a resulted decrease in the flexibility of the bristles leads to a deterioration of the traceablity of the bristles relative to the rotor shaft 120. Therefore, such a forced contact causes the wear of both the rotor shaft 120 and the brush bristles 101.
FIG. 16 illustrates the front view of the inner diameter free end face 105 of the brush seal 109 given in FIG. 15.
When the process fluid enters between the brush bristles 101 in FIG. 15 and FIG. 16, the individual brush bristles 101 arranged as shown in FIG. 16 when viewed from the inner circumferential side are forced to move aside so that gaps are created between the adjacent brush bristles 101. These gaps cause a leakage of the process fluid. Furthermore, the brush bristles 101 once being pushed aside while being pressed against the backing plate 102 due to the process fluid pressure cannot easily restore the original position. Therefore the seal performance is decreased.
Under this circumstance, when a portion of the brush seal 109 is assumed to mate with the rotor shaft 120 in a press fitting manner, the opposite side relative to the portion develops a wide clearance C between the rotor shaft 120 and the free end face 105 of the brush bristles 101. This clearance C causes a leakage of the process fluid from between the brush seal 109 and the rotor shaft 120.
There has been a brush seal device 100B as a relative art of the present invention, as shown in FIG. 18. The seal device 100B of FIG. 18 provides a seal between the higher pressure region P1 and the lower pressure region P2 by means of a plurality of thin layered sheet seal 209 which are laminated along the circumferential direction of the rotor shaft 120.
The outer circumferential portion of the sheet seal 209 is brazed to form a mounting portion 104 by means of which the sheet seal 209 is disposed in the installation groove portion of the casing 110. A backing plate 102 is disposed adjacent the side face of the sheet seal 209 in the lower pressure region P2 while a retaining plate 103 is disposed adjacent the opposite side face in the higher pressure region P1. These two plates 102, 103 provide a support for the sheet seal 209 at its both sides.
However, with a sheet seal 209 thus arranged in which the thin plates are pressed against the decentered rotor shaft 120, the sheet seal 209 forcibly arched cannot easily undertake an elastic deformation and it results in a large spring coefficient corresponding to the elastic deformation. Therefore this leads to a problem of difficulty in following the eccentricity of the rotor shaft 120. In order to avoid this problem, a modest clearance between the free end face of the sheet seal 209 and the outer diameter surface of the rotor 120 is assumed. This clearance in turn deteriorates the seal performance of the device due to a leakage of the process fluid through it.
In the sheet seal 209, a plurality of simple flat plates are laminated in parallel to the direction of the action of the process fluid pressure. Therefore, the process fluid pressure acting in that direction easily leaks through a lamination gap between the individual flat plates and this ends up with a sealing problem against the process fluid.
In addition, the poor flexible nature of the lamination structure results in a fast wear of the free end face 105 of the sheet seal 209.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to improve the seal performance of a brush seal.
Another goal is to enhance the elastic deformation capability of a brush seal against a pressing force given by a rotor shaft and to decrease a wear of the brush seal caused by the rotor shaft.
Yet another goal is to achieve a good traceability of a brush seal relative to a rotor shaft when the rotor shaft rotates while being in contact with the brush seal and to prevent an energy loss for driving the rotor shaft under such a contact state. A further goal is to prevent a decrease of a seal performance of the brush seal due to fluctuations of the rotor shaft.